| With the development of underground engineering,shield tunnel construction in dense urban areas will encounter obstacles such as reinforced concrete pile foundations.When the tunnel project cannot avoid the pile foundation,it is less efficient to rely solely on the direct cutting of reinforced concrete by the tunnel boring machine.The tool wears a lot,and problems such as edge curling,chipping,and steel-winding cutter head frequently occur.It is a good idea to combine high-pressure jet technology with shield tools.The abrasive jet is used to erode the steel bar to cause pre-damage,and then the tool is used to cut the damaged area,which can quickly and effectively break the reinforced concrete while reducing the loss when the tool collides with the steel bar.In the future,it has great potential to solve the problem of urban underground shield tunneling and breaking obstacles.The high-pressure abrasive jet technology has a broad practical foundation in the mechanical field,but the research on the abrasive jet cutting pile technology under shield loading conditions is currently in its infancy,and there are the following key issues that need to be studied:①This technology requires abrasive jets to efficiently erode and damage steel bars.In the past,the research goal of water milling reinforced concrete was to remove the concrete without destroying the steel bars.Therefore,there is still a lack of relevant research on the effect of the abrasive jet on the erosion of the steel bars and the damage mechanism.②Under shield loading conditions,the abrasive water jet needs to have the characteristics of "high moving speed,large target distance,and reciprocating cutting",which is different from the "low moving speed,small target distance,and one-time cutting" condition in traditional machining and drilling fields.③Under the shield working environment,the reinforced concrete pile is in a state of mud flow solid immersion,and the weakening effect of immersion on the abrasive jet remains to be studied;④As a new construction method,there are few researches on the evaluation of the erosion efficiency of the jet fluid,the design ideas and principles of the perfect abrasive jet cutter head configuration have not yet been formed,and the construction control technology is not yet mature.To solve the problem of high-efficiency abrasive jet-assisted cutting of reinforced concrete piles under complicated conditions such as shield tunneling and submergence and difficult working conditions such as high traverse speed and reciprocating cutting.Research the effect and parameter optimization of high-pressure abrasive jet cutting reinforced concrete piles in shield tunneling.Carry out the experimental research on the characteristics of abrasive jet cutting for steel and concrete respectively,observe the change of the kerf shape under the conditions of high traverse speed and large target distance reciprocating cutting,clarify the kerf expansion law and damage mechanism of the abrasive jet cutting concrete and steel bar,and interpret The mutual influence between the parameters,the cutting efficiency evaluation of different effective parameter combinations to determine the key control parameters that affect the cutting effect.On this basis,the cutting effect and influencing factors of the high-pressure abrasive jet of reinforced concrete piles under submerged conditions are studied,the true crushing ability of abrasive jets in shield tunneling is explored,the key influencing factors influencing cutting efficiency are clarified,and the effect of mud submerged conditions on erosion efficiency is clarified.influence level.Finally,the experimental research is summarized,and recommendations for the control technology and parameter selection of abrasive water jet cutting piles are formed,and the minimum cutting depth specific energy is used as an index to establish the optimal parameter combination of abrasive jets arranged on the cutter head,combining experimental research and shield tunneling Reasonable excavation technology recommendations are formed by experience.The main research work and results of this paper are as follows:The main research work and results of this paper are as follows:（1）The order of the sensitivity of cutting depth parameters in the study of mixed abrasive jet erosion of concrete after deployment is traverse speed>cutting times>standoff distance>pump pressure.The influence gap between the various parameters is small,and cannot be ignored for the cutting depth.As the cutting depth increases,the damage mechanism of cutting is transformed from fracture and crushing of aggregate particles to local high tensile stress and crack propagation.The response between the control parameters and the cutting depth is expressed as:the kerf depth increases exponentially with the decrease of the traverse speed,and decreases with the increase of the standoff distance,especially after the limit standoff distance node is exceeded,it rapidly decreases.With the increase of the number of cuts,the expansion speed of the kerf is reduced significantly.（1）The test of abrasive jet erosion of concrete under the conditions of high traverse speed（3～12m/min）,large target distance（5～15cm）,and high pump pressure（160～380MPa）was carried out,and the control variables were obtained for cutting The influence law of depth and cutting width,determining the traverse speed,cutting times,and target distance are the key factors affecting cutting efficiency.The study found that the damage mechanism of concrete under the condition of high moving speed and multiple cutting is gradually transformed from crushing and erosion of aggregate and cementitious materials into tensile stress cracking in concrete.Under the condition of high traverse speed,increasing the traverse speed and increasing the number of cuts can improve the cutting efficiency.There is a threshold target distance when the abrasive jet erodes the concrete.If the threshold target distance is exceeded,the erosion ability will rapidly decrease.（2）The test of abrasive jet erosion of steel bars under the conditions of high traverse speed,large target distance and high pump pressure was carried out to obtain the influence law of control variables on cutting depth,cutting width and cutting volume,and determine the number of cuts and pump pressure.,The traverse speed is the key factor that affects the cutting efficiency.The study found that the failure process of the steel bar has a process of "two sides first and then the middle".The damage mechanism is:steel erosion is affected by both removal and cutting action and deformation and wear.The change of the specific gravity of the two effects is determined by the mechanical properties and shape of the steel.There is a critical pressure at which the steel bar begins to fail,about 150 MPa.As the number of cuts increases,the volumetric efficiency of the cutting slowly decreases,and the efficiency of the cutting depth decreases significantly.（3）Experiments on abrasive jet cutting reinforced concrete piles under submerged and non-submerged conditions were carried out,and the cross-sectional shape of the abrasive jet erosion of concrete under different working conditions was drawn,and the law of interaction between steel and concrete was obtained.The influence of mud covering on the erosion effect of reinforced concrete is analyzed emphatically,and the influence of submerged conditions on the cutting effect is quantified.Under submerged conditions,the average erosion depth of concrete is reduced by 25-35%,and steel reinforcement is reduced by 30%-50%.The order of the key parameters that affect the cutting parameters under submerged conditions is pump pressure,target distance,cutting times,and traverse speed.（4）According to the structural characteristics of the shield cutter head,suggestions are made on the position relationship between the jet nozzle and the cutter,the position relationship between the jet nozzle,and the selection and arrangement of the cutter head.A specific energy model based on the cutting depth of steel bars is established and key control parameters are optimized,and the tunneling process proposal of "controlling thrust,alternating cutting,slow thrust,low speed,and maintaining attitude" is proposed for the tunneling process of abrasive jet-assisted shield tunneling through pile foundation. |
